The field of the invention is that of mobile telecommunications networks that offer procedures for mobility between cells.
The invention applies in particular to UMTS Terrestrial Radio Access Networks (UTRAN) and GSM Edge Radio Access Networks (GERAN).
In such networks it is known that mobile telecommunications terminals in a mobility situation attempt to connect to cells whose identifiers are contained in a list that they manage and that contains the identities of the cells on which measurements are to be effected by the mobile terminal.
Using a known mechanism, the mobile terminals effect these measurements (in particular field measurements) on each of the cells identified in the list, and they select the cell that gives the maximum level for these measurements.
According to the Third Generation Partnership Project (3GPP) standard, this list is stored in the mobile terminal in a CELL-INFO-LIST variable.
The list of cells to be measured by the mobile is constructed from information about the adjacent cells received by the mobile terminal, either from its attachment cell (i.e. the cell on which it is camped when a reselection mechanism is being applied) or, in the situation of a transfer between cells (connected mode mobility or handover mechanism), from an entity of the network known as a radio network controller (RNC) that controls the base stations.
When the mobile terminal is in idle mode, the list of adjacent cells received by a mobile terminal is broadcast by the network in a System Information Block 11 (SIB 11) message.
When the mobile is in connected mode (i.e. communicating), the list of adjacent cells is sent to it in a Measurement Control message.
The invention is particularly directed to networks offering procedures for mobility to restricted-access cells, i.e. cells to which access is reserved to a closed user group.
Restricted-access cells are typically used in a residential or professional context.
The above-described mechanisms by which the network informs a mobile terminal about its adjacent cells cannot be used to offer the terminal a list of its adjacent restricted-access cells.
The list of adjacent cells contained in the SIB 11 and SIB 12 messages depends neither on the mobile terminal to which it is broadcast or sent nor on the user of that terminal. In other words, these messages are identical for all terminals attached to the same serving cell or the same RNC.
Consequently, in the current state of the art, if these messages were used to communicate restricted-access cell identifiers, those identifiers would also be received by terminals not entitled to access those cells, which would have two disadvantages.
Firstly, in order to attempt to connect to them, the mobile terminals would effect measurements on those cells that would be of no utility, since access to them would in the end be refused.
Secondly, only a limited number of identifiers can be contained in the list managed by a terminal (32 in intra-frequency in the case of the CELL-INFO-LIST variable). Now, it is reasonable to think that this number would be relatively small in geographical areas in which a large number of restricted-access cells might be installed, and that it is highly desirable not to clutter the list with identifiers of cells to which access by the terminal is entirely impossible because it is prohibited.